1. Field of the Invention
The present invention relates to an application and manufacturing method of porous graphite, more particularly to a heat sink and manufacturing method of porous graphite.
2. Description of the Prior Art
Up till now, electronic products which have been developed in a miniaturization tendency have achieved nanometer scale chip fabrication; however, the generated heat and radiating heat intensity have kept on increasing as a result. Therefore, it is now an urgent issue to develop material with high performance in heat dissipating so as to solve heat dissipating problems derived from electronic products requiring high power density.
Carbon foam has several excellent properties such as low density, fire resistance, low thermal expansion coefficient and chemical erosion resistance and may be used in heat conduction or heat insulation dependent on different carbon crystal alignment or foaming structure. Carbon foam has been characterized in excellent heat transmission and interconnected open voids which provide a very large specific surface area for heat transmission and heat dissipation. Therefore, carbon foam has been highly regarded as one of the novel heat dissipating material with high potential to solve heat dissipating problems of modern electronics products.
Carbon foam is now mainly produced by heat-treating a mesophase pitch developed by ORNL (Oak Ridge National Laboratory). First, a mesophase pitch precursor is heated, in an oxygen-free environment above its softening point, about 50° C. Once the pitch has melted, the furnace pressure is elevated and the temperature is raised at a controlled rate. While the pitch is molten, it begins to evolve low molecular weight species. These volatile gases form bubbles at nucleation sites on the bottom and sides of the crucible and rise to the top, beginning to orient the mesophase crystals in the vertical direction. With time, a significant amount of the mesophase crystals are oriented vertically. The foamed mesophase is carbonized by heating to between 600° C. and 1000° C. to yield a relatively pure carbon foam. The carbon foam is converted to a graphitic foam by heat treatment to more than 2800° C. under an argon purge.
The porosity of the carbon foam is usually greater than 80% (as illustrated in FIG. 5) so that voids of the carbon foam are interconnected but such high porosity results in insufficient physical strength. The carbon foam may be broken when applied with greater stress and may therefore have limitation in application. In addition, there is still room for improvement in manufacturing process and cost for carbon foam manufacturing using heat-treating a mesophase pitch.
To sum up, it is now a current goal to develop a device based on novel graphite material which provides good heat conduction and improved physical strength.